In the manufacture of semiconductor devices and other products, ion implantation systems are used to impart impurities, known as dopant elements, into semiconductor wafers, display panels, or other workpieces. Typical ion implantation systems or ion implanters treat a workpiece with an ion beam in order to produce n- or p-type doped regions, or to form passivation layers in the workpiece. When used for doping semiconductors, the ion implantation system injects a selected ion species to produce the desired extrinsic material. Typically, dopant atoms or molecules are ionized and isolated, sometimes accelerated or decelerated, formed into a beam, and swept across a wafer. For example, the ion beam may be manipulated to “scan” the wafer, or the wafer may be translated with respect to a generally stationary ion beam. Dopant ions then physically bombard and enter the surface of the wafer, and subsequently come to rest below the surface.
A typical ion implantation system is generally a collection of sophisticated subsystems, wherein each subsystem performs a specific action on the dopant ions. Dopant elements can be introduced in gas form or in a solid form that is subsequently vaporized, wherein the dopant elements are positioned inside an ionization chamber and ionized by a suitable ionization process. For example, the ionization chamber is maintained at a low pressure (e.g., a vacuum), wherein a filament is located within the chamber and heated to a point where electrons are created from the filament source. Negatively-charged electrons from the filament source are then attracted to an oppositely-charged anode within the chamber, wherein during the travel from the filament to the anode, the electrons collide with the dopant source elements (e.g., molecules or atoms) and create a plurality of positively charged ions from the source elements.
Generally, in addition to desired dopant ions being created, other non-desirable positive ions are also created. Accordingly, the desired dopant ions are selected from the plurality of ions by a process referred to as analyzing, mass analyzing, selection, or ion separation. Selection, for example, is accomplished by utilizing a mass analyzer that creates a magnetic field, wherein ions from the ionization chamber travel through the magnetic field. The ions generally leave the ionization chamber at relatively high speeds, wherein the ions are consequently bent into an arc by the magnetic field. The radius of the arc is dictated by the mass of individual ions, speed, and the strength of the magnetic field. Accordingly, an exit of the analyzer permits only one species of ions (e.g., the desired dopant ions) to exit the mass analyzer.
Subsequently, the desired ions may be transported through ion optical elements that serve the purpose of manipulating the ions to focus or affect the trajectory of the ions, wherein the ion optical elements generally match the angles of the ion trajectory to the needs of the implant. Alternatively, the ion energies are changed to meet the needs of the implant, or the ions are deflected in order to cover a workpiece of a relatively large size. Any or all of these manipulation effects can be utilized by the ion implantation system to achieve a desired implant to the workpiece.
Accordingly, the dopant ions are then directed towards a target workpiece that is situated in an end station. Consequently, the dopant ions (e.g., in the form of a “pencil” or spot beam) impact the workpiece with a particular beam intensity and emittance, wherein the beam intensity is generally a measure of the number of particles impacting the workpiece per unit time as a function of position on the workpiece, and the emittance is an angular distribution (e.g., angle of incidence) of the ion beam as a function of the position. Generally, it is desirable that the beam intensity and emittance be substantially uniform and at expected or desired values.
Typically, it is desirable to determine the emittance of the ion beam in both horizontal and vertical directions with respect to the surface of the workpiece. However, conventional emittance measurement devices that are capable of measuring emittance in both horizontal and vertical directions are either substantially complex (thus adding complexity to the ion implantation system), and/or generally require a movement of the measurement device in both horizontal and vertical directions in order to determine both horizontal and vertical angles of incidence of the ion beam. Accordingly, a need currently exists for an improved system and method for determining the emittance of the ion beam, wherein the system and method provide a less-complex, single-axis movement of the measurement device to achieve acceptable emittance measurements.